Voicecoil concept

[NemoAndrea]

I considered a voicecoil-based mechanism for the fine Z-focus mechanism. Voicecoils are attractive, as they can deliver fast and precise response, which is useful in trying to minimise time spent focussing.

Voicecoils also seem more sensible for linear actuation, as there is something a bit 'silly' to taking a rotational actuator and converting it to linear motion with e.g. ballscrew. The downside is that voicecoil actuators do not have any 'holding torque', meaning that to maintain a steady position they must continously draw power. Not a huge concern for light assemblies, but it means for heavy assemblies fighting gravity it is a tricky part.

Combining a voice coil actuator (VCA) with a flexure seems like the nicest way to go about it, but a linear rail will do just as well. I made a little concept for this:

Unfortunately, there does not seem to be a huge list of suppliers that provide these, making them niche and expensive products. Of course a unit from speakers could be used but I would much prefer a characterised actuator (with a spec list).

In the ideal case with a frictionless linear rail guide system, the VCA would need a lifting force of at least 0.8N (weight of the objective), which should probably be taken to about 1.6N minimum actuation force to be safe. Adding a flexure mechanism would increase the minimum force required even further.

The Thorlabs VCA are a little bit too expensive (~320 euro for an actuator that meets force requirements). Similar products from H2W Technologies seemed to similary be too expensive to fit within the budget of the Medjed project.